DESCRIPTION: (Applicant's Abstract) This study is designed to elucidate the epidemiologic risk factors for prevalent and incident HIV-1 infections among opiate users in northern Thailand, and to determine whether methadone maintenance is associated with reduced relapse to narcotics use as compared to methadone-assisted detoxification on an outpatient basis. These studies will be accomplished by interviewing and screening all first admissions to the Northern Drug Dependence Treatment Center in Mae Rim (Chiang Mai Province), Thailand, a facility operated by the Department of Medical Services, Ministry of Public Health. Approximately 1,750 first admissions are seen per year, and will comprise the prevalence study. Currently, about 25% of injectors are HIV infected on admission and 8% of opium smokers have antibody to HIV. A prospective cohort study will be conducted among persons seeking readmission to the NDDTC over a two year period, as well as opiate users who relapse following treatment and are seen in an outpatient opiate detoxification program or who reside in village settings within 100 km of the NDDTC. A total of 800 relapsed opiate users will be followed for two years to study endpoints, and we will determine the incidence of HIV infection. We will also conduct a randomized controlled trial of outpatient methadone maintenance vs. methadone assisted detoxification among 480 opiate users seeking treatment for drug abuse, with the primary study endpoint being relapse to opiate use; secondary outcomes include incident sexually transmitted diseases and drug use-related HIV risk behaviors; HIV incidence will be measured as well. These data on the epidemiology of HIV infection among drug users have relevance for other southeast Asian countries experiencing a dramatic HIV epidemic, in which opiate use plays an important role directly through sharing of injection equipment, and as a bridge to the general heterosexual population through unprotected sexual behavior.